Lubricant seals, such as those seals used to seal between an axle of a vehicle and a bore in a wheel hub are often not visible after they are installed and the only way generally available to determine an ineffectively installed seal is by visual observation of lubricant which leaks past the seal.
When heavy assemblies, such as a dual wheel assembly for a vehicle, are installed onto the axle of a vehicle, such as an over-the-road tractor or trailer, the assembly is often carefully aligned with the axle with the seal positioned in a bore of the wheel hub and then forced axially onto the axle. Sometimes, due to the velocity with which the assembly is forced onto the axle, the lubricant seal, due to inertia, does not stop when the wheel assembly is forced to stop by being seated on the bearings. The resulting over-travel or over-installation of the seal axially along the shaft or axle causes the seal to partially withdraw from the bore in the wheel hub and consequently renders the assembly susceptible to leakage.
A second cause of a leaking seal is improper placement or seating of the seal into the bore of the assembly prior to installation of the assembly onto the axle. Here again, as with the over-installed seal, the assembly is susceptible to leakage due either to a lack of sealing between the seal and the wheel hub or due to a misalignment of the components of the seal itself whereby upon rotation of the wheel assembly relative to the axle the skewed position of the seal relative to the longitudinal axis of the axle and the bore mounted coaxial with the axle forces the seal components into an unsealed relationship with each other to enable undesireable leakage of lubricant from the hub of the wheel assembly.